This invention relates to methodologies and techniques for the design, fabrication and use of a fluidic system incorporating means by which electric fields are applied to carry out the assembly of micron to nanoscale materials. By way of example, the inventions serve to form microelectronic, micromechanical, microoptical and mixed function devices or assemblies both in two dimensions and three dimensions. This invention also relates to associated microelectronic and optoelectronic devices, systems, and manufacturing platforms which provide electric field transport, and optionally, selective addressing of components, including self-assembling, nanostructures, sub-micron and micron sized components to selected locations on the device itself or onto other substrate materials.
The fields of molecular electronics/photonics and nanotechnology offer immense technological promise for the future. Nanotechnology is defined as a projected technology based on a generalized ability to build objects to complex atomic specifications. Drexler, Proc. Natl. Acad. Sci USA, 78:5275-5278, (1981). Nanotechnology generally means an atom-by-atom or molecule-by-molecule control for organizing and building complex structures all the way to the macroscopic level. Nanotechnology is a bottom-up approach, in contrast to a top-down strategy like present lithographic techniques used in the semiconductor and integrated circuit industries. The success of nanotechnology may be based on the development of programmable self-assembling molecular units and molecular level machine tools, so-called assemblers, which will enable the construction of a wide range of molecular structures and devices. Drexler, xe2x80x9cEngines of Creation,xe2x80x9d Doubleday Publishing Co., New York, N.Y. (1986).
Present molecular electronic/photonic technology includes numerous efforts from diverse fields of scientists and engineers. Carter, ed., xe2x80x9cMolecular Electronic Devices II,xe2x80x9d Marcel Dekker, Inc, New York, N.Y. (1987). Those fields include organic polymer based rectifiers, Metzger et al., xe2x80x9cMolecular Electronic Devices II,xe2x80x9d Carter, ed., Marcel Dekker, New York, N.Y., pp. 5-25 (1987), conducting conjugated polymers, MacDiarmid et al., Synthetic Metals, 18:285 (1987), electronic properties of organic thin films or Langmuir-Blogett films, Watanabe et al., Synthetic Metals, 28:C473 (1989), molecular shift registers based on electron transfer, Hopfield et al., Science, 241:817 (1988), and a self-assembly system based on synthetically modified lipids which form a variety of different xe2x80x9ctubularxe2x80x9d microstructures. Singh et al., xe2x80x9cApplied Bioactive Polymeric Materials,xe2x80x9d Plenum Press, New York, N.Y., pp. 239-249 (1988). Molecular optical or photonic devices based on conjugated organic polymers, Baker et al., Synthetic Metals, 28:D639 (1989), and nonlinear organic materials have also been described. Potember et al., Proc. Annual Conf. IEEE in Medicine and Biology, Part 4/6:1302-1303 (1989).
However, none of the cited references describe a sophisticated or programmable level of manufacturing self-organization or self-assembly. Typically, the actual molecular component which carries out the electronic and/or photonic mechanism is a natural biological protein or other molecule. Akaike et al., Proc. Annual Conf. IEEE in Medicine and Biology, Part 4/6:1337-1338 (1989). There are presently no examples of a totally synthetic programmable self-assembling molecule which produces an efficient electronic or photonic structure, mechanism or device.
Progress in understanding self-assembly in biological systems is relevant to nanotechnology. Drexler, Proc. Natl. Acad. Sci USA, 78:5275-5278 (1981), and Drexler, xe2x80x9cEngines of Creation,xe2x80x9d Doubleday Publishing Co., New York, N.Y. (1986). Areas of significant progress include the organization of the light harvesting photosynthetic systems, the energy transducing electron transport systems, the visual process, nerve conduction and the structure and function of the protein components which make up these systems. The so-called bio-chips described the use of synthetically or biologically modified proteins to construct molecular electronic devices. Haddon et al., Proc. Natl. Acad. Sci. USA, 82:1874-1878 (1985), McAlear et al., xe2x80x9cMolecular Electronic Devices II,xe2x80x9d Carter ed., Marcel Dekker, Inc., New York N.Y., pp. 623-633 (1987).
Some work on synthetic proteins (polypeptides) has been carried out with the objective of developing conducting networks. McAlear et al., xe2x80x9cMolecular Electronic Devices,xe2x80x9d Carter ed., Marcel Dekker, New York, N.Y., pp. 175-180 (1982). Other workers have speculated that nucleic acid based bio-chips may be more promising. Robinson et al., xe2x80x9cThe Design of a Biochip: a Self-Assembling Molecular-Scale Memory Device,xe2x80x9d Protein Engineering, 1:295-300 (1987).
Great strides have also been made in the understanding of the structure and function of the nucleic acids, deoxyribonucleic acid or DNA, Watson, et al., in xe2x80x9cMolecular Biology of the Gene,xe2x80x9d Vol. 1, Benjamin Publishing Co., Menlo Park, Calif. (1987), which is the carrier of genetic information in all living organisms (See FIG. 1). In DNA, information is encoded in the linear sequence of nucleotides by their base units adenine, guanine, cytosine, and thymidine (A, G, C, and T). Single strands of DNA (or polynucleotide) have the unique property of recognizing and binding, by hybridization, to their complementary sequence to form a double stranded nucleic acid duplex structure. This is possible because of the inherent base-pairing properties of the nucleic acids: A recognizes T, and G recognizes C. This property leads to a very high degree of specificity since any given polynucleotide sequence will hybridize only to its exact complementary sequence.
In addition to the molecular biology of nucleic acids, great progress has also been made in the area of the chemical synthesis of nucleic acids. This technology has developed so automated instruments can now efficiently synthesize sequences over 100 nucleotides in length, at synthesis rates of 15 nucleotides per hour. Also, many techniques have been developed for the modification of nucleic acids with functional groups, including: fluorophores, chromophores, affinity labels, metal chelates, chemically reactive groups and enzymes. Smith et al., Nature, 321:674-679 (1986); Agarawal et al., Nucleic Acids Research, 14:6227-6245 (1986); Chu et al., Nucleic Acids Research, 16:3671-3691 (1988).
An impetus for developing both the synthesis and modification of nucleic acids has been the potential for their use in clinical diagnostic assays, an area also referred to as DNA probe diagnostics. Simple photonic mechanisms have been incorporated into modified oligonucleotides in an effort to impart sensitive fluorescent detection properties into the DNA probe diagnostic assay systems. This approach involved fluorophore and chemilluminescent-labeled oligonucleotides which carry out Fxc3x6rster nonradiative energy transfer. Heller et al., xe2x80x9cRapid Detection and Identification of Infectious Agents,xe2x80x9d Kingsbury et al., eds., Academic Press, New York, N.Y. pp. 345-356 (1985). Fxc3x6rster nonradiative energy transfer is a process by which a fluorescent donor group excited at one wavelength transfers its absorbed energy by a resonant dipole coupling process to a suitable fluorescent acceptor group. The efficiency of energy transfer between a suitable donor and acceptor group has a 1/r6 distance dependency (see Lakowicz et al., xe2x80x9cPrinciples of Fluorescent Spectroscopy,xe2x80x9d Plenum Press, New York, N.Y., Chap. 10, pp. 305-337 (1983)).
As to photonic devices, they can generally be fabricated in dense arrays using well developed micro-fabrication techniques. However, they can only be integrated over small areas limited by the relatively high defect densities of the substrates employed. In order to be useful and economically viable, these devices must in many cases, be used within large area silicon integrated circuits. A good example of this issue is the vertical cavity surface emitting lasers. To address many potential applications, it would be highly desirable to integrate these devices with large area silicon IC""s. A major obstacle in the integration of these new devices with silicon is the existence of material and geometrical incompatibilities. These devices need to be integrated on silicon in large sparse arrays with minimal performance degradation, and without affecting the underlying silicon circuits. Over the past years, a number of component assembly technologies have been extensively investigated regarding the integration of such compound semiconductor devices on silicon. These include hybrid flip-chip bonding or epitaxial lift-off and other direct bonding methods. Although these hybrid technologies have made significant progress and several component demonstrations have shown the viability of these techniques, these methods do not address the problem of geometrical incompatibility. That is, the dimensions with which the specialty devices are fabricated on their mother substrate must be conserved when they are coupled onto the host substrate. This makes the integration of small area devices on large area components economically unfeasible.
A major obstacle in the integration of these new devices with silicon is the existence of material and geometrical incompatibilities. These devices need to be integrated on silicon in large sparse arrays with minimal performance degradation, and without affecting the underlying silicon circuits. Over the past years, a number of component assembly technologies have been extensively investigated regarding the integration of such compound semiconductor devices on silicon. These include hybrid flip-chip bonding or epitaxial lift-off and other direct bonding methods. Although these hybrid technologies have made significant progress and several component demonstrations have shown the viability of these techniques, these methods do not address the problem of geometrical incompatibility. That is, the dimensions with which the specialty devices are fabricated on their mother substrate must be conserved when they are coupled or grafted onto the silicon board.
Efforts have been made to fabricate self-assembling microstructures onto a substrate through fluid transport. For example, in U.S. Pat. No. 5,783,856, entitled xe2x80x9cMethod for Fabricating Self-Assembling Microstructuresxe2x80x9d, methods and apparatus are disclosed which utilized microstructures having shaped blocks which self-align into recessed regions located on a substrate such that the microstructure becomes integral with the substrate. A slurry containing multiple devices is then poured over the substrate bearing the recessed regions such that the microstructures selectively engage with the substrate.
The prior art has no integration technique that is capable of creating a sparse array of devices distributed over a large area, when the devices are originally fabricated densely over small areas. This makes large area components made up from integration of micron size devices economically unfeasible. To solve this problem, the electronics industry employs a hierarchy of packaging techniques. However, this problem remains unsolved when a regular array of devices is needed on large areas with a relatively small pitch. This problem is probably most noticeable through the high cost associated with the implementation of matrix addressed displays, where the silicon active matrix consists of small transistors that need to be distributed over a large area. Thus, prior art microfabrication techniques limit devices to small area components where a dense array of devices are integrated. However, there are a number of important applications that could benefit from specialty devices being integrated more sparsely over large areas.
One possible method for removing the geometrical limitations is the further development of semiconductor substrate materials to the point where their defect densities approaches that of silicon. This is a long and expensive process that requires incremental progress. A second approach is the development of special robots capable of handling micron and sub-micron size devices and able to graft them to appropriate places. This also seems impractical because the grafting process will remain sequential where one device may be grafted after another, requiring impractical processing times. In any case, both of these approaches may be limited to motherboard dimensions on the order of 10 cm.
With regard to memories, data processing engines have been physically and conceptually separated from the memory which stores the data and program commands. As processor speed has increased over time, there has been a continuous press for larger memories and faster access. Recent advances in processor speed have caused system bottlenecks in access to memory. This restriction is critical because delays in obtaining instructions or data may cause significant processor wait time, resulting in loss of valuable processing time.
Various approaches have been taken to solve these concerns. Generally, the solutions include using various types of memory which have different attributes. For example, it is common to use a relatively small amount of fast, and typically expensive, memory directly associated with the processor units, typically called cache memory. Additionally, larger capacity, but generally slower, memory such as DRAM or SRAM is associated with the CPU. This intermediate memory is often large enough for a small number of current applications, but not large enough to hold all system programs and data. Mass storage memory, which is ordinary very large, but relatively inexpensive, is relatively slow. While advances have been continually made in improving the size and speed of all types of memory, and generally reducing the cost per bit of memory, there remains a substantial need especially to serve yet faster processors.
For the last 20 years most mass storage devices have utilized a rotating memory medium. Magnetic media have been used for both xe2x80x9cfloppyxe2x80x9d (flexible) disks or xe2x80x9chardxe2x80x9d disk drives. Information is stored by the presence or absence of magnetization at defined physical locations on the disk. Ordinarily, magnetic media are xe2x80x9cread-writexe2x80x9d memories in that the memory may be both written to and read from by the system. Data is written to or read from the disk by heads placed close to the surface of the disk.
A more recent development in rotating mass storage media are the optical media. Compact disks are read only memory in which the presence or absence of physical deformations in the disk indicates the data. The information is read by use of a focused laser beam, in which the change in reflectance properties from the disk indicate the data states. Also in the optical realm are various optical memories which utilize magnetooptic properties in the writing and reading of data. These disks are both read only, write once read many (xe2x80x9cWORMxe2x80x9d) drives and multiple read-write memories. Generally, optical media have proved to have a larger storage capacity, but higher costs per bit and limited write ability, as compared with magnetic media.
Several proposals have been made for using polymers for electronic based molecular memories. For example, Hopfield, J. J., Onuchic, J. N. and Beratan, D. N., xe2x80x9cA Molecular Shift Registerxe2x80x9d, Science, 241, p. 817, 1988, discloses a polymer based shift register memory which incorporates charge transfer groups. Other workers have proposed an electronic based DNA memory (see Robinson et al, xe2x80x9cThe Design of a Biochip: A Self-Assembling Molecular-Scale Memory Devicexe2x80x9d, Protein Engineering, 1:295-300 (1987)). In this case, DNA is used with electron conducting polymers for a molecular memory device. Both concepts for these molecular electronic memories do not provide a viable mechanism for inputting data (write) and for outputting data (read).
Molecular electronic memories have been particularly disappointing in their practical results. While proposals have been made, and minimal existence proofs performed, generally these systems have not been converted to commercial reality. Further, a specific deficiency of the system described above is that a sequential memory is typically substantially slower than a random access memory for use in most systems.
The optical memories described above suffer from the particular problem of requiring use of optical systems which are diffraction limited. This imposes size restrictions upon the minimum size of a data bit, thereby limiting memory density. This is an inherent limit in systems which store a single bit of data at a given physical memory location.
Further, in all optical memory systems described above, the information is stored on a bit-by-bit basis, such that only a single bit of data is obtained by accessing a giving physical location in memory. While word-wide memory access systems do exist, generally they store but a single bit of information at a given location, thereby requiring substantially the same amount of physical memory space whether accessed in a bit manner or word-wide manner.
While systems have generally increased in speed and storage density, and decreased in cost per bit, there remains a clear gap at present between processor speed and system requirements. See generally, xe2x80x9cNew Memory Architectures to Boost Performancexe2x80x9d, Tom R. Halfhill, Byte, July, 1993, pp. 86 and 87. Despite the general desirability of memories which are faster, denser and cheaper per bit, and the specific critical need for mass memory which can meet the demands of modem day processor systems speed, no completely satisfactory solution has been advanced heretofore. The fundamental limitations on the currently existing paradigms cannot be overcome by evolutionary enhancements in those systems.
Despite the clear desirability for new and improved apparatus and methods in this field, no optimal solution has been proposed previously.
Increasingly, the technologies of communication, information processing, and data storage are beginning to depend upon highly-integrated arrays of small, fast electronic and photonic devices. As device sizes scale down and array sizes increase, conventional integration techniques become increasingly costly. The dimensions of photonic and electronic devices permit the use of electronic assembly and/or molecular biological engineering for the integration and manufacturing of photonic and electronic array components. This invention also relates to associated microelectronic and optoelectronic devices, systems, and manufacturing platforms which provide electric field transport and selective addressing of self-assembling, nanostructures, sub-micron and micron size components to selected locations on the device itself or onto other substrate materials.
More broadly, the invention in this respect relates to a method for the fabrication of micro scale and nanoscale devices comprising the steps of fabricating first component devices on a first support, releasing at least one first component device from the first support, transporting the first component device to a second support, and attaching the first component device to the second support. In particular, electrostatic, electrophoretic and electroosmotic forces may be employed to transport,,position and orient components upon a suitably designed substrate either in sequential steps or in parallel. Optionally, nucleic acid hybridization or other forms of molecular biological or other forms of reversibly binding systems may be employed to promote self-assembly and self-sorting of materials as components within or between components of these assemblies. A further aspect of this invention involves carrying out the various electric filed assisted assembly processed under low gravity conditions, which may improved the overall performance.
This invention relates to the means of enabling micron and nanoscale assembly in a fluid medium by use of electric fields for placement of components and subassemblies. This invention also encompasses the design, composition and manufacture of components, assembly substrates or platforms and component delivery systems as well as the composition of the fluid medium. This technology lends itself to scaling dimensions ranging from the molecular (sub-nanometer) to the micron. Furthermore, the use of self-organizing or self-assembling molecules such as polynucleic acids can serve to augment the overall utility of this approach. This broad flexibility is unique to this technology and represents a novel application of electric fields, devices and materials. The heterogeneous assembly of microelectronic, microoptical and micromechanical components upon an integrated silicon circuit represents one such use of this approach. Thus, this invention relates to the employment of electric fields, the nature and scale of materials to be assembled, the electrical and chemical properties of the assembly surface or environment, the means by which electrical interconnects may be formed and the potential utility of such assembled devices.
The electric fields relating to this invention can be either electrostatic, electrophoretic, electroosmotic, or dielectrophoretic in nature. In addition, the resultant forces used for component positioning may be comprised of various combinations of these. In application, a fluid medium, typically aqueous in composition, would be deposited onto the assembly surface. This surface has one or more microlocations which govern the application of these electric fields through the fluid medium. Devices or components for assembly are added to the fluid medium and then are targeted by control of the electric fields to defined positions upon the assembly surface. Transport is accomplished by interactions between the device and the nature and effects of the forces engendered by the electric fields. In particular, if net charges are present upon the components or devices, electrophoretic or possibly electrostatic forces would be factors governing movement of the materials. Alternatively, if no net charge is present upon these materials, forces such as electroosmosis which enables bulk fluid movement or dielectrophoresis may be employed to maneuver and locate the devices at specific locations upon the surface. In certain circumstances, both electrophoretic and electroosmotic (or other combinations of forces) may work in combination to guide position and orientation of component assembly.
The use of electric fields has been described for the movement of biological molecules, typically nucleic acids or proteins, for the purpose of analysis, diagnosis or separation. See, e.g., U.S. Pat. No, 5,605,662. These inventions are more particularly directed to the assembly of micron to sub-micron to nano-scale assembly of components to form functional composite devices or sub-assemblies. Such heterogeneous integration using these fields represents a novel means by which assembly technology can progress to new dimensions and materials. One advantage of this non-mechanical xe2x80x9cpick-and-placexe2x80x9d assembly technology is the ability to handle a variety of component shapes and sizes upon a common platform. In addition, the forces employed are self-governing in so far as the movement of the components is regulated by the components themselves, i.e. their shape, their dimensions and their surface charge and not dependent upon an external mechanical device. This feature thereby lessens or minimizes the likelihood of possible mechanical damage to possibly fragile components during placement.
Key to the utilization of this technology is an appropriately designed and composed assembly platform. Such a platform contains electrodes on the assembly surface enabling the formation of electric fields that establish the forces necessary for transport of devices and components during the assembly process. These electrodes may either be at the point to which the components are to be located or adjacent to these locations (i.e. xe2x80x9cdrivexe2x80x9d electrodes). The latter form of electrodes would typically not serve as electrical connection points to the assembly, but rather as aids to the assembly process. Other electrodes may serve both roles, operating both as driving points for assembly and as locations for electrical contact between the components and the underlying assembly platform. Combinations of both drive electrodes and xe2x80x9ccontactxe2x80x9d electrodes may be present at any one assembly location or throughout the assembly platform.
Also, the surface of the assembly platform may be adopted or modified through lithographic techniques to present stop points or recesses into which the components can be electronically positioned. These arresting points by themselves are constructed such that, in the absence of applied electronic control, movement of devices and components as well as their orientation at these positions would not be possible.
The composition of the assembly surface is also modifiable in order to more precisely match the needs of the assembly process. In particular, the surface can be covered with a permeable layer composed of hydrogels, SiO2, or other related materials suitable for providing sites of attachment for molecules useful for anchoring devices, components, nanoscale and molecular scale materials as well as serving as a means of distancing the assembly site from the reactive zone set up when electrolysis of water occurs.
The other form of coating would be one which modifies the inherent charge of the surface and velocity of fluid, either augmenting, neutralizing or reversing electroosmotic flow along this surface. In contrast to the permeation layer whose functionality and role is useful at or adjacent to working electrodes, this surface modifying coat would be functioning not at the active electrodes per se but at the assembly surface between electrode locations.
A new class of components or devices would be designed for use with this system. That is, these components would contain features both enabling derivatization with suitable chemistry in order to provide charge and/or sites of attachment for molecules providing charge and/or self-assembly functionality, e.g. nucleic acids, and would be constructed in such a fashion as to provide contact features enabling electric connection between the component and either the underlying assembly platform or other devices or materials attached to this component itself. Contacts could be so constructed as to remove the need for specific orientation of the device on the assembly platform. That is, by use of concentric ring electrodes on the component device, the need to orient the device upon the assembly platform is removed by having an infinite number of orientations while in that plane being suitable. Alternatively, the outside faces of the component or device might be shaped such as to enable locating into modified assembly surface features, e.g., use of matching shaped devices with corresponding surface depressions or stops. Such designs would serve to provide alignment of electrical and mechanical contacts for the devices and components to the assembly platform and to other components, devices, and sub-assemblies.
An important feature would the mechanism to deliver components and materials to the assembly platform. A microfluidic delivery head comprised of both the means to contain components prior to application to the working platform and the counter electrode necessary to set the appropriate electric field geometry aiding assembly is one such design that may be employed. Each of these two aspects represents novel application (and modification) of existing technology, e.g. microfluidics and electrode design. In addition, the means of fluidic delivery itself may be combined with the counter electrode such that devices are either electrophoretically or electroosmotically transported through the device head into fluid overlaying the assembly platform. In an alternative embodiment, a device platform may receive a motherboard and provide the return electrode or conduction path for electrode sites on the motherboard. In this way, the number of electrodes on the motherboard may be reduced, and the device simplified. The device platform may contain sources of component devices, such as substrates from which component devices are subject to lift-off.
Electrical or mechanical connections between assembled components may take place either serially, as each set of components is arranged or as a final step in the assembly process. These connections depend in part upon the surfaces to be joined and the type of joint to be formed. In particular, we have discovered that metals can be electrodeposited through permeation layers to form electrical contact to materials positioned at these locations. In addition, conductive materials, e.g. organic polymers, could be used to coat the polynucleotide scaffolding employed for self-assembly.
Some potential applications for these techniques are: (1) Fabricating light emitter arrays over large surfaces; (2) assembly of two or three-dimensional photonic crystal structures; (3) two and three dimensional high density data storage materials, devices and systems; and (4) manufacturing of various hybrid-integrated components including flat panel displays, wireless/RF integrated devices, lab on a chip devices, microcantiliver sensor devices, atomic force microscope devices, integrated MEMS/optical/microelectronic devices, integrated microscopic analytical and diagnostic devices, and compact/handheld medical diagnostic devices and systems.
As photonics plays an increasingly important role in information processing, communication and storage systems it will deliver faster, smaller, more power efficient, and functionally versatile integrated systems at lower cost. New fabrication technologies including nanostructure fabrication, integration and self-assembly techniques are used. As device dimensions shrink to submicron levels, it becomes important to utilize the inventive concepts employing molecular biological engineering concepts and principles as manufacturing techniques for the fabrication of integrated photonic and electronic devices.
In one particular implementation, light emitting diodes (LEDs) may be fabricated on a support and removed therefrom utilizing a lift-off technique. Component devices such as the LEDs may then be placed on the motherboard or target device generally in the target position through use of electroosmotic force. Once the component device has been appropriately placed, substantially permanent electrical contact with the motherboard or target device is then effected. In the preferred embodiment, the component device is subject to a soldering technique, such as through a solder reflow technique.
In yet another aspect of this invention, methods for the assembly of devices in a low gravity environment are provided. More particularly, electrical transport, preferably electrostatic or electrophoretic, but also possibly electroosmotic or dielectrophoretic, may be utilized in a low gravity environment to place devices from a source of devices onto target structures or motherboards and to then affixed and activate those devices on that target device or motherboard.
Accordingly, it is one object of this invention to enable micron and sub-micron (including nanotechnology) through use of electrical transport and placement of component devices from a source to target locations, and to affix and, if required by the nature of the device, to activate the device through cooperation with the target device or motherboard.
In yet another aspect, these inventions seek to employ electrical forces, such as electrostatic, electrophoretic and electroosmotic forces, to transport, position and orient components upon a designed substrate.
In yet another aspect of this invention, the methods and apparatus are designed to optimally provide parallel actions, such as through the parallel transport of various component devices to multiple target locations.
It is an object of this invention to enable nanotechnology and self-assembly technology by the development of programmable self-assembling molecular construction units.